>>>>>It does occur over pretty much every fret on the fretboard
Being made of wood, the neck's going to move around a bit (weather, temp etc). That will result in a change of neck relielf and, in turn, string height.
My guess is that the neck has become straighter and consequently, the strings are now closer to the fret board than they were previously.
By coincidence, it appears to have moved to where it should be, as the buzz is all over the neck.
I'd be turning my attention to string height.
With the Bass in the play position, and using a 6" steel rule, measure the height of each string at around the 17th fret (between bottom of strings and top of the fret). Aim for around 3/32" on each, consistent with no buzz up and down the neck (from around the 4th fret to the end of the neck). The string height might have to be raised more or perhaps lowered further...depending on how hard you play. Don't worry about any buzz at the first few frets at this stage (if any).
Optional: What I do at this stage is now lower the G string saddle screws 1/4 turn each and lower the A and D proportionately to meet the G (for smoother transition ascross the strings).
Finally, if there's buzz at the first few frets (normally with the D and G strings) slowly add a little relief to the neck untill eliminated. Move the truss wheel to the left, one hole at a time, as you look from the heel towards the headstock. Tune to pitch after each truss wheel adjustment.
Finally, what Mark said about cars is absolutely correct
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